Increase accuracy of isAsyncFunction when followed by a backslash

Issue #1382

Author: marijnh

acorn/src/statement.js

@@ -70,7 +70,7 @@ pp.isAsyncFunction = function() {
   return !lineBreak.test(this.input.slice(this.pos, next)) &&
     this.input.slice(next, next + 8) === "function" &&
     (next + 8 === this.input.length ||
-     !(isIdentifierChar(after = this.input.charCodeAt(next + 8)) || after > 0xd7ff && after < 0xdc00))
+     !(isIdentifierChar(after = this.input.charCodeAt(next + 8)) || after === 92 || after > 0xd7ff && after < 0xdc00))
 }
 
 pp.isUsingKeyword = function(isAwaitUsing, isFor) {

test/tests-asyncawait.js

@@ -3549,3 +3549,5 @@ test("async () => class { x = await }", {}, {ecmaVersion: 2024})
 
 testFail("async () => class { x = await }", "Cannot use keyword 'await' outside an async function (1:24)",
          {ecmaVersion: 2024, sourceType: "module"})
+
+testFail("async function\\u1111() { }", "Unexpected token (1:20)", {ecmaVersion: 8})